BIOCHEMISTRY, CELL AND MOLECULAR BIOLOGY TEST

Time—170 minutes

180 Questions

Directions: Each of the questions or incomplete statements below is followed by five suggested answers or completions. Select the one that is best in each case and then completely fill in the corresponding space on the answer sheet.

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  1. Regulation of metabolic pathways includes all of the following except:
  2. Regulation of key enzymes in a pathway.
  3. Control transcription and translation to regulate enzyme amounts.
  4. Tissue-specific enzymes and receptors.
  5. Reciprocal synthetic and degradative pathways utilize the same set of enzymes.
  6. Compartmentation of reciprocal synthetic and degradative pathways.
  1. Which of the following statements concerning cell adhesion complexes is INCORRECT?
  2. Tight junctions are a type of communicating junction.
  3. Adherens junctions are a type of anchoring junction.
  4. Selectins form anchoring junctions.
  5. Claudins are a component of tight junctions.
  6. Connexons are a component of gap junctions.
  1. Which of the following statements concerning homeotic (Hox) genes is INCORRECT?
  2. A Hox gene taken from one organism can function in another organism.
  3. The order of Hox gene expression along the embryo matches the order of Hox genes on the chromosome.
  4. Mutations in Hox genes can create flies with legs where their antennae should be.
  5. Hox genes encode cell surface receptors.
  6. Antennapedia is a Hox gene.
  1. Meiosis can occur
  2. in all organisms
  3. only when an organism is diploid
  4. only in multicellular organisms
  5. only in haploid organisms
  6. only in single-celled organisms
  1. At the isoelectric pH of a tetrapeptide:
  2. the amino and carboxyl termini are not charged.
  3. two internal amino acids of the tetrapeptide cannot have ionizable R groups.
  4. the total net charge is zero.
  5. there are four ionic charges.
  6. only the amino and carboxyl termini contribute charge.
  1. In the diagram below, the plane drawn behind the peptide bond indicates the:
  1. plane of rotation around the Cα—N bond.
  2. absence of rotation around the C—N bond because of its partial double bond character.
  3. region of steric hindrance determined by the large C¬O group.
  4. theoretical space between –180° and +180° that can be occupied by the  and  angles in the peptide bond.
  5. region of the peptide bond that contributes to a Ramachandran plot.
  1. Which of the following situations would result in an increase in ketone body synthesis?
  2. High insulin/glucagon ratio
  3. High citrate levels in the cytosol
  4. High levels of fructose-2,6-bisphosphate
  5. Low oxaloacetate levels in the mitochondria
  6. Low acetyl CoA levels in the mitochondria
  1. Which of the following statements concerning tumor suppressor genes is most accurate?
  2. In a normal individual, mutation of one copy of a tumor suppressor gene leads to cancer.
  3. In a normal individual, the development of cancer requires mutation of one copy of a tumor suppressor gene in one cell plus the mutation of the other copy of the gene in another cell.
  4. In a normal individual, the development of cancer requires mutation of one copy of a tumour suppressor gene plus the mutation of the other copy of the gene in the same cell.
  5. In a normal individual, the development of cancer requires mutation of one copy of a tumor suppressor gene in one cell plus the mutation of the same copy of the gene in another cell.
  6. Mutations in tumor suppressor genes are not passed onto the offspring because the individual dies.
  7. Given the following reactions:


What is the ΔGo’ value for the reaction:

FADH2+½ O2FAD +H2O

(ΔGo’ = -nFΔEo’, where F = faraday’s constant=23 kcal/volt mole e-)

  1. +46 kcal/mol
  2. -46 kcal/mol
  3. +23 kcal/mol
  4. -23 kcal/mol
  5. -11.5 kcal/mol
  1. The pyruvate dehydrogenase complex is INCORRECTLY described by which of the following?
  2. Produces CO2, NADH and acetyl Coenzyme A
  3. Is phosphorylated in the presence of insulin
  4. Requires thiamine pyrophosphate to carry carbons
  5. Can be directly inhibited by NADH and Acetyl Coenzyme A
  6. Is a target for arsenic poisoning
  1. In 1928, Griffith injected S (smooth) bacteria into mice, and the mice died. When he injected living R (rough) bacteria into mice, the mice lived. When he injected heat-killed smooth bacteria into mice, the mice lived. What was the result when he mixed heat-killed S bacteria with live R bacteria and injected this mixture into mice?
  2. a. the mice lived
  3. b. the mice died indicating that heat-killed S bacteria came back to life
  4. c. the mice lived, and living S bacteria could be obtained from the tissues of living mice
  5. d. the mice died, indicating that DNA replicated semi-conservatively
  6. e. the mice died, and living S cells could be isolated from the tissues of the dead mice
  1. The regulation of cholesterol synthesis involves all of the following EXCEPT:
  2. glucagon activates HMG-CoA reductase
  3. cholesterol inhibits the synthesis of HMG-CoA reductase
  4. cholesterol increases the degradation of HMG-CoA reductase
  5. the dephosphorylated form of HMG-CoA reductase is active
  6. cholesterol inhibits the synthesis of the LDL receptor
  1. At the end of meiosis I, each chromosome consist of
  2. a homologous chromosome pair
  3. four copies of a DNA molecule
  4. one copy of a DNA molecule
  5. two chromatids
  6. a pair of polar microtubules
  1. Which of the molecules shown below can be made directly from pyruvate?


  1. Molecules 1 and 4
  2. Molecules 2 and 3
  3. Molecules 1, 2, and 4
  4. Molecules 1, 3, and 4
  5. Molecules 1, 2, 3, and 4
  1. A patient is taking a drug that must be activated by cytochrome p450 enzymes to be fully efficacious. A mutation that inactivates which of the following enzymes would most directly affect the patient’s ability to respond to this medication?
  2. A. pyruvate carboxylase
  3. B. glucose 6-phosphate dehydrogenase
  4. C. pyruvate kinase
  5. D. malate dehydrogenase
  6. E. citrate synthase
  1. A mutation in the lac operator sequence prevents the lac repressor from binding. What would you expect to see in bacteria harbouring this mutation?
  2. The bacteria would have difficulty growing in media containing only lactose.
  3. In the presence of glucose and lactose, the polycistronic message for the lac operon would accumulate to its maximum level.
  4. The catabolite activator protein would no longer be able to bind.
  5. cAMP levels would be constitutively high.
  6. When both glucose and lactose are absent, lac permease activity would be higher in the mutant than in normal bacteria.
  1. Individual cell migration is most accurately described by which of the following sequence of events?
  2. (1) Actin polymerization extends from focal contacts in the direction of migration; (2) New focal contacts are made and the treadmilling actin network engages them to continue the cell extension; (3) Actin depolymerization at the minus end of the treadmilling network detaches the cell from focal contacts at the rear.
  3. (1) Actin polymerization extends from focal contacts in the direction of migration; (2) New focal contacts are made and the treadmilling actin network engages them to continue the cell extension; (3) Myosin II contraction detaches the cell from focal contacts at the rear.
  4. (1) Actin polymerization extends the cell forward in the direction of migration; (2) Focal contacts are disassembled at the front of the cell to allow it to move over the substratum (3) Myosin II contraction also detaches the cell from focal contacts at the rear.
  5. (1) Actin polymerization extends the cell forward in the direction of migration; (2) Focal contacts are disassembled at the front of the cell to allow it to move over the substratum; (3) Actin depolymerization at the minus end of the treadmilling network also detaches the cell from focal contacts at the rear.
  6. (1) Individual actin filaments are stabilized by actin binding proteins; (2) Myosin II thick filaments move the actin filament past one another to extend the actin filament system forward; (3) As the actin filaments slide forward they engage focal contacts to pull the rest of the cell forward.
  1. Which of the following statements do NOT account for the differences in complexity between eukaryotic transcriptional regulation and bacterial transcriptional regulation?

i. Eukaryotic DNA is packaged into chromatin.

ii. Eukaryotic RNA Polymerase II cannot activate transcription on its own.

iii. Eukaryotic Shine-Dalgarno sequences generate complex patterns of transcriptional regulation.

iv. Eukaryotic gene regulatory proteins act at a distance.

v. Eukaryotic gene regulatory proteins are not regulated by ligand binding.

  1. i, ii, iii
  2. ii, iv
  3. iii, v
  4. i, ii, iv
  5. ii
  1. In an experiment that attempts to identify origins of replication in yeast, randomly selected DNA fragments are introduced into a plasmid that has a selectable marker such as the HIS gene (histidine). Yeast that have plasmids with various DNA fragments introduced are then plated on a selective medium (i.e. without histidine). What would be expected in these experiments?
  2. Yeast cells that have plasmids with DNA fragments without putative origins of replication should grow on media without histidine.
  3. The strain of yeast used for these experiments should be able to grow in the absence of histidine.
  4. In order to replicate, the plasmids used for these experiments do not need a DNA fragment containing an origin of replication.
  5. Yeast cells that have integrated the plasmid into their chromosome will be able to grow on media without histidine, regardless of whether they have a putative origin of replication or not.
  6. Yeast cells must be plated on medium with histidine to determine if they have plasmids with DNA fragments containing putative origins of replication.
  1. Which of the following oligonucleotides will dissociate at the lowest temperature?
  2. ACGTACGTACGT

TGCATGCATGCA

  1. TGCGACGCTGAG

ACGCTGCGACTC

  1. ACTGCTGGACCT

TGACGACCTGGA

  1. TGCATGCATGCA

ACGTACGTACGT

  1. AATGCTTACTGTA

TTACGAATGACAT

  1. In the presence of high glucagon levels, what is the status of glycogen phosphorylase?
  2. Is phosphorylated, active, and sensitive to glucose 6-phosphate levels
  3. Is unphosphorylated, active, and sensitive to glucose 6-phosphate levels
  4. Is phosphorylated, inactive, and sensitive to glucose 6-phosphate
  5. Is phosphorylated, active, and sensitive to glucose levels
  6. Is unphosphorylated, inactive, and sensitive to glucose levels
  1. The cadherin-cadherin binding mechanism is most accurately described by which of the following sequence of events?
  2. (1) cis-dimerization promotes receptor straightening; (2) calcium promotes heterophilic, trans-interactions between the receptors; (3) the receptors interact with actin.
  3. (1) cis-dimerization promotes receptor straightening; (2) calcium promotes homophilic, trans-interactions between the receptors; (3) the receptors form large clusters.
  4. (1) Calcium promotes receptor straightening; (2) cis-dimerization promotes homophilic, trans-interactions between the receptors; (3) the receptors form large clusters.
  5. (1) Calcium promotes receptor straightening; (2) cis-dimerization promotes heterophilic, trans-interactions between the receptors; (3) the receptors form large clusters.
  6. (1) trans-interactions between the receptors promote cis-dimerization; (2) calcium promotes receptor clustering; (3) the receptors interact with actin.
  1. Assuming Hardy-Weinberg equilibrium, the genoypte frequency of heterozygotes, if the frequency of the two alleles at the gene being studied are 0.6 and 0.4, will be:
  2. 0.80
  3. 0.64
  4. 0.48
  5. 0.32
  6. 0.16
  1. One of the reasons for glycosylation of proteins is to serve as a tag for unfolded proteins in the endoplasmic reticulum (ER). What is the role of glycosyl transferase in this process?
  2. It removes the 3 glucose residues that are found at the end of N-linked oligosaccharides.
  3. It is embedded in the membrane of the ER and binds to unfolded proteins, thereby preventing them from aggregating.
  4. It binds to unfolded proteins in the lumen of the ER and adds glucose molecules, which then bind to calnexin.
  5. It is the enzyme that adds a large preformed oligosaccharide onto asparagine residues in proteins.
  6. It glycosylates calnexin and calreticulin allowing them to interact and help to properly fold proteins that are unfolded.
  1. You have digested a plasmid with EcoRI and expect to obtain fragments 5000 bp, 3000 bp, and 2000 bp in length. You want to clone the 2000 bp fragment into another vector and to be able to do this you need to obtain 1 μg of the desired 2000 bp fragment. Given that you will be using plasmid DNA at a concentration of 0.5 μg/μl, how many μl of plasmid DNA should you add to your EcoRI digest?
  2. 2 μl
  3. 5 μl
  4. 10 μl
  5. 4 μl
  6. 8 μl
  1. Of the 20 standard amino acids, only ______is not optically active. The reason is that its side chain ______.
  2. proline; forms a covalent bond with the amino group.
  3. alanine; is a simple methyl group.
  4. glycine; is unbranched.
  5. alanine; contains only hydrogen.
  6. glycine; is a hydrogen atom.
  1. A hydronium ion:
  2. is a hydrated proton.
  3. is a hydrated hydrogen ion
  4. has the structure H3O+.
  5. is the usual form of one of the dissociation products of water in solution.
  6. All of the above are true.
  1. The gene coding for a soluble protein that is normally targeted to the lumen of peroxisomes is mutated so that an ER signal sequence is added to the encoded protein at the N-terminal end. The normal peroxisomal signalling sequence remains in the encoded protein. What is the most likely final destination of the protein?
  2. Lysosomes.
  3. The nucleus.
  4. The protein would be secreted from the cell.
  5. Peroxisomes.
  6. The Golgi apparatus.
  1. What is the function of Ran-GEF?
  2. It binds to nucleoporins ensuring that cargo is transported out of the nucleus.
  3. It promotes the exchange of GDP for GTP on Ran.
  4. It binds to the nuclear export signal of the cargo protein.
  5. It transports the empty nuclear export receptor into the nucleus.
  6. It enhances the intrinsic GTPase activity of Ran.
  1. The preparation of DNA for mitosis is most accurately described by which set of events?
  2. (1) During S phase, the chromatids assemble kinetochores to interact with microtubules; (2) During prophase, condensins compact the chromatids and cohesins hold the chromatids together; (3) DNA is then duplicated to form sister chromatids.
  3. (1) During S phase, condensins compact the chromatids and cohesins hold the chromatids together; (2) During prophase, the chromatids assemble kinetochores to interact with microtubules; (3) DNA is then duplicated to form sister chromatids.
  4. (1) During S phase, DNA is duplicated to form sister chromatids; (2) During prophase, cohesins compact the chromatids and condensins hold the chromatids together; (3) The chromatids then assemble kinetochores to interact with microtubules.
  5. (1) During S phase, cohesins compact the chromatids and condensins hold the chromatids together; (2) During prophase, the chromatids assemble kinetochores to interact with microtubules; (3) DNA is then duplicated to form sister chromatids.
  6. (1) During S phase, DNA is duplicated to form sister chromatids; (2) During prophase, condensins compact the chromatids and cohesins hold the chromatids together; (3) The chromatids then assemble kinetochores to interact with microtubules.
  1. Which of the following molecules is a product of the urea cycle that can be converted back to a substrate of the urea cycle?
  2. aspartate
  3. carbamoyl phosphate
  4. fumarate
  5. malate
  6. oxaloacetate
  7. The process of fatty acid synthesis involves all of the following except:
  8. A large multi-enzyme complex
  9. Acetyl CoA carboxylase
  10. NADPH
  11. Malonyl CoA
  12. CAT I (carnitine acyl transferase I)
  1. One of the in vitro muscle systems required the addition of calcium ions. What is the critical role of calcium with respect to muscle contraction?
  2. Calcium is a necessary co-factor for ATPase activity of the myosin head.
  3. Calcium binds to tropomyosin, which sends a signal to troponin to pull tropomyosin out of its actin binding groove.
  4. Calcium allows for the proper dynamics of the large titin protein.
  5. Calcium binds to troponin, which releases tropomyosin into its normal binding groove so that the myosin heads can bind.
  6. Calcium activates calmodulin, which sends a signal to the troponin complex to pull tropomyosin out of its actin binding groove, so the actin can bind to the myosin heads.
  1. In a highly basic solution, pH = 13, the dominant form of glycine is:
  2. NH2—CH2—COOH.
  3. NH3+—CH2—COOH.
  4. NH2—CH2—COO⁻.
  5. NH3+—CH2—COO⁻.
  6. NH2—CH3+—COO⁻.
  1. The single most important contribution to the stability of a protein's conformation appears to be the:
  2. sum of free energies of formation of many weak interactions among the hundreds of amino acids in a protein.
  3. entropy increase from the decrease in the number of ordered water molecules forming a solvent shell around a protein.
  4. sum of free energies of formation of many weak interactions between a protein's polar amino acids and surrounding water.
  5. maximum entropy increase from ionic interactions between the ionized amino acids in a protein.
  6. stabilizing effect of hydrogen bonding in a protein between the carbonyl group of one peptide bond and the amino group of another, as indicated by —C¬O|||H—N—.

  1. Skeletal muscle cells that have a functional insulin signalling pathway are treated with insulin. An hour later, a protein extract is made from the cells. Proteins in the extract are separated by SDS-PAGE and then the gel is blotted. The blot is incubated with antibodies that detect phosphoserine, phosphothreonine and phosphotyrosine residues in proteins. The blot is washed and then incubated with an appropriate secondary antibody to allow for detection of the primary antibodies. Which of the following proteins would you expect to detect on the blot? Give a complete list.

1. insulin receptor

2. IRS-1

3. Grb2

4. Phosphatidylinositol 3-kinase (PI 3-kinase)

5. PDK1

6. protein kinase B (PKB)

  1. 2, 3, 4
  2. 1, 2, 3, 5, 6
  3. 4, 5, 6
  4. 1, 2, 5, 6
  5. 2, 4
  1. Which type of regular light microscopy is the BEST for visualizing transparent internal structures in living cells?
  2. Bright-field microscopy.
  3. Transmission electron microscopy.
  4. Nomarski Imaging (Differential Interference Contrast).
  5. Fluorescence microscopy.
  6. Confocal microscopy.
  1. Suppose one were provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicated once in the presence of this radioactive base?
  2. One of the daughter cells but not the other will have radioactive DNA
  3. Neither of the two daughter cells will be radioactive
  4. All four bases of the DNA would be radioactive
  5. Radioactive thymine would pair with non-radioactive guanine
  6. DNA in both daughter cells will be radioactive
  1. What is the correct enzyme name for the reaction drawn below?
  2. acetoacetate dehydrogenase
  3. β-hydroxybutyrate reductase
  4. β-hydroxybutyrate dehydrogenase
  5. acetoacetate reductase
  6. β-hydroxybutyrate synthase
  1. Vitamin deficiencies may affect many metabolic pathways due to the requirement of cofactors in enzymatic reactions. The Pentose Phosphate Pathway (PPP) can be run in one of four modes, depending on the specific purpose or product(s) needed (listed below). Which of these four modes of the PPP would NOT be affected by thiamine deficiency?

Mode #1: NADPH + Ribose-5-P